How do u tell if new rubber parts are compatible with DOT 5 fluid? U knd of wonder when the guy at the NAPA store says " Yeah, I think they are"
I guess you could try contacting the manufacturer of the parts or look at their web site for a FAQ section.
That said, I refurbished by rear cylinders using off the shelf rubber and installed new off the shelf front cylinders and master cylinder in my car over 10 years ago. I think the parts were largely Wagner but I can't guarantee it. Especially for the rubber parts in the cylinders I bought new.
One of the refurbished wheel cylinders has just started to leak, the rest are fine. So that off the shelf stuff from a decade ago seems to have been compatible with silicone brake fluid. And my guess is that if I had sleeved the rear cylinders back then they'd still be good too.
There are only two issues on compatibility that I have consistently heard of:
1. Mixing DOT-5 and either DOT-3 or DOT-4 in the same system. Seems like all the rubber failures on DOT-5 conversions have been associated with this. Starting with DOT-5 after a total rebuild seems to be the way to go.
2. Hydraulic brake light switches are rumored to be killed by DOT-5. That said, I re-used my old switch (the one that was on the car when I got in 35 years ago) and it is still working fine after 10 years of use with DOT-5.
I've not had any problems with DOT-5 fluid in about 10 years, it won't harm your paint either. I suppose you could take a rubber piece and submerge it in fluid for 30 days to see how it does.
I knew a fellow once that had a free source for DOT-5 and he used it as dressing on his tires.
Jim
I have used Dot 5 silicone. Its big plus is that it does not absorb water and therefore lessens the problem of electrolytic action between dissimilar metals in the braking system. The downside is its high price, lack of availability in an emergency situation, and that it aerates easily making bleeding a challenge. One other issue is silicone contamination from any spills may make painting in the shop area difficult.(for example if you blew the lines clear with compressed air, then silicone would settle on everything nearby.)
I have several cars with regular fluid. No problems in 15 to 20 years. I have three vehicles with silicone. One needed new cylinders in the front because moisture jammed up the pistons. (this would have happened with regular fluid too). One presently has a leaky cylinder, a routine maintenance item to be sure, and the third, a 28 Chrysler, seems to have air in the system which I cannot bleed out. I do not blame any problems on the silicone, but I do not see any real advantages either.
This is the same answer to a related subject on Dot Brake Fluids.
Early in my carrier I twisted wrenches for the government and have converted several vehicles over to Dot-5 with only a couple of soft pedal problems. We warranted the master cylinder with no other problems. The biggest mistake made is flushing the system out especially with alcohol you Will be replacing rubber components Guaranteed!! You can just bleed the Dot 5 through, and replace nothing unless it needs replacing anyway. Now would be a great time to inspect every thing & replace items in question. Make sure you do a though job of bleeding as it tends to turn the petroleum based fluid into mud down the road if you did not get it all out. A power bleeder is the best way if you have access to one and make sure the fluid coming out of the bleeder is clean, that way you should not have any residual old fluid. But if you experience that, I just clean the mud out with a clean cloth and rebleed till you get the blue or red fluid flowing clean!. The only advantage you would gain is corrosion proofing and that ant all bad at all!! The petroleum based fluid can absorb moisture causing lines to corrode from within over time, the silicone will not absorb moisture and that's a good thing! The other advantage to Dot 5 is brake heat dissipation from repeated hard applications that is probably not the way you are driving your car. Now if you are experiencing brake fade do to heat then you will notice a difference. The question I guess is it worth the extra cost converting over? Or if it ain't broke don't fix it?
Here is a article that is a must read that should help.
Battle of the DOTs
DOT 3-4 Verses DOT 5. Which brake fluid should I use?
As a former materials engineering supervisor at a major automotive brake system supplier, I feel both qualified and obligated to inject some material science facts into the murky debate about DOT 5 verses DOT 3-4 brake fluids. The important technical issues governing the use of a particular specification brake fluid are as follows:
1. Fluid compatibility with the brake system rubber, plastic and metal components.
2. Water absorption and corrosion.
3. Fluid boiling point and other physical characteristics.
4. Brake system contamination and sludging.
Additionally, some technical comments will be made about the new brake fluid formulations appearing on the scene.
First of all, it's important to understand the chemical nature of brake fluid. DOT 3 brake fluids are mixtures of glycols and glycol ethers. DOT 4 contains borate esters in addition to what is contained in DOT 3. These brake fluids are somewhat similar to automotive anti-freeze (ethylene glycol) and are not, as Dr. Curve implies, a petroleum fluid. DOT 5 is silicone chemistry.
Fluid Compatibility
Brake system materials must be compatible with the system fluid. Compatibility is determined by chemistry, and no amount of advertising, wishful thinking or rationalizing can change the science of chemical compatibility. Both DOT 3-4 and DOT 5 fluids are compatible with most brake system materials except in the case some silicone rubber external components such as caliper piston boots, which are attacked by silicon fluids and greases.
Water absorption and corrosion
The big bugaboo with DOT 3-4 fluids always cited by silicone fluid advocates is water absorption. DOT 3-4 glycol based fluids, just like ethylene glycol antifreezes, are readily miscible with water. Long term brake system water content tends to reach a maximum of about 3%, which is readily handled by the corrosion inhibitors in the brake fluid formulation. Since the inhibitors are gradually depleted as they do their job, glycol brake fluid, just like anti-freeze, needs to be changed periodically. Follow BMW's recommendations. DOT 5 fluids, not being water miscible, must rely on the silicone (with some corrosion inhibitors) as a barrier film to control corrosion. Water is not absorbed by silicone as in the case of DOT 3-4 fluids, and will remain as a separate globule sinking to the lowest point in the brake system, since it is more dense.
Fluid boiling point
DOT 4 glycol based fluid has a higher boiling point (446F) than DOT 3 (401F), and both fluids will exhibit a reduced boiling point as water content increases. DOT 5 in its pure state offers a higher boiling point (500F) however if water got into the system, and a big globule found its way into a caliper, the water would start to boil at 212F causing a vapor lock condition [possible brake failure -ed.]. By contrast, DOT 3 fluid with 3% water content would still exhibit a boiling point of 300F. Silicone fluids also exhibit a 3 times greater propensity to dissolve air and other gasses which can lead to a "spongy pedal" and reduced braking at high altitudes.
DOT 3 and DOT 4 fluids are mutually compatible, the major disadvantage of such a mix being a lowered boiling point. In an emergency, it'll do. Silicone fluid will not mix, but will float on top. From a lubricity standpoint, neither fluids are outstanding, though silicones will exhibit a more stable viscosity index in extreme temperatures, which is why the US Army likes silicone fluids. Since few of us ride at temperatures very much below freezing, let alone at 40 below zero, silicone's low temperature advantage won't be apparent. Neither fluids will reduce stopping distances.
With the advent of ABS systems, the limitations of existing brake fluids have been recognized and the brake fluid manufacturers have been working on formulations with enhanced properties. However, the chosen direction has not been silicone. The only major user of silicone is the US Army. It has recently asked the SAE about a procedure for converting from silicon back to DOT 3-4. If they ever decide to switch, silicone brake fluid will go the way of leaded gas.
Brake system contamination
The single most common brake system failure caused by a contaminant is swelling of the rubber components (piston seals etc.) due to the introduction of petroleum based products (motor oil, power steering fluid, mineral oil etc.) A small amount is enough to do major damage. Flushing with mineral spirits is enough to cause a complete system failure in a short time. I suspect this is what has happened when some BMW owners changed to DOT 5 (and then assumed that silicone caused the problem). Flushing with alcohol also causes problems. BMW brake systems should be flushed only with DOT 3 or 4.
If silicone is introduced into an older brake system, the silicone will latch unto the sludge generated by gradual component deterioration and create a gelatin like goop which will attract more crud and eventually plug up metering orifices or cause pistons to stick. If you have already changed to DOT 5, don't compound your initial mistake and change back. Silicone is very tenacious stuff and you will never get it all out of your system. Just change the fluid regularly. For those who race using silicone fluid, I recommend that you crack the bleed screws before each racing session to insure that there is no water in the calipers.
New developments
Since DOT 4 fluids were developed, it was recognized that borate ester based fluids offered the potential for boiling points beyond the 446F requirement, thus came the Super DOT 4 fluids - some covered by the DOT 5.1 designation - which exhibit a minimum dry boiling point of 500F (same as silicone, but different chemistry).
Additionally, a new fluid type based on silicon ester chemistry (not the same as silicon) has been developed that exhibits a minimum dry boiling point of 590F. It is miscible with DOT 3-4 fluids but has yet to see commercial usage.
This is my first post as a new member so I wish to apologize for being so lengthy.
Herb
I first came across dot 5 brake fluid in 1977, that year harley davidson changed over to it... we had a lot of problems with it swelling up and causing the master cylinders to build pressure to the point it would lock up the wheel..... not a good idea on a motorcycle..... we did find the swelling was a vendor related problem.. not all brake rubber was affected... since the mid 80s most all vendors rubber has been changed to work with the dot 5.....this does not apply to foriegn made rubber brake parts.....I E china , tiwan etc... I may still have the orgional service bulletin if anyone whats to know which vendors were involved